Detection of interannual population trends in seven herbivores from a West African savannah: a comparison between dung counts and direct counts of individuals

In West Africa, whether in forests or savannahs, most of the large mammal species have a scattered spatial distribution. Monitoring their population size represents a logistic, financial, theoretical challenge because counting of transects is not appropriate, unlike elsewhere in Africa. In this study, we (i) analyse the patterns of interannual (2006-2008) changes in population density of seven sympatric species of savannah herbivores in a protected area of Burkina Faso with two alternative methods: dung counts versus direct counts and (ii) quantify the economic costs for these two methods. The seven species of mammals we considered are the following: Hippotragus equinus, Alcelaphus busephalus, Sylvicapra grimmia, Tragelaphus scriptus, Ourebia ourebi, Kobus ellipsiprymnus and Phacochoerus africanus. A distance methodology was used to generate estimates with both methods. There were significant correlations between estimates of mammal density obtained using dung counts and direct counts, and an analysis of covariance revealed that the interannual trends in population densities were consistently detected with both methods. In addition, the dung count method costs 55% less. Thus, our study documents that dung counts can be used as a proxy of population size fluctuations for the seven studied species, offering a methodological alternative that is much less expensive, less sophisticated in terms of equipment compared to other methods and that can be performed by field staff with moderate professional qualification. We suggest that standardized campaigns of dung count surveys may be applied to all protected areas and savannah in Burkina Faso, West Africa, in order to improve evidence-based, large-scale conservation and management planning in the region.